[css-ui-4] Remove ''outline-color: invert'' value

As per #9199

Author: frivoal

css-ui-4/Overview.bs

@@ -396,7 +396,7 @@ Outline Colors: the 'outline-color' property</h3>
 
 	<pre class="propdef">
 	Name: outline-color
-	Value: auto | [ <<color>> | <<image-1D>> ] | invert
+	Value: auto | [ <<color>> | <<image-1D>> ]
 	Initial: auto
 	Applies to: all elements
 	Inherited: no
@@ -410,36 +410,30 @@ Outline Colors: the 'outline-color' property</h3>
 	as well as the following keywords:
 
 	<dl dfn-type=value dfn-for=outline-color>
-		<dt><dfn>invert</dfn>
-		<dd>
-			the user agent is expected to perform a color inversion on the pixels on the screen.
-			This is a common trick to ensure the focus border is visible,
-			regardless of color background.
-
-			Conformant UAs may ignore the ''outline-color/invert'' value
-			on platforms that do not support color inversion of the pixels on the screen.
-
-			If the UA does not support the ''outline-color/invert'' value,
-			then it must reject that value at parse-time, and
-			the initial value of the 'outline-color' property
-			is the ''color/currentColor'' keyword.
-
 		<dt><dfn>auto</dfn>
 		<dd>
 			When 'outline-style' is ''outline-style/auto'',
-			''outline-color: auto'' represents the [=accent color=].
+			''outline-color: auto'' computes to ''outline-style/auto''
+			and represents the [=accent color=].
 
-			When 'outline-style' is not ''outline-style/auto'',
-			''outline-color: auto'' computes to another value (see below).
+			Otherwise,
+			''outline-color: auto'' computes to ''currentColor''.
 	</dl>
 
-	The computed value for ''outline-color: auto'' is ''outline-color/auto''
-	if 'outline-style' is ''outline-style/auto'',
-	and ''invert'' otherwise--
-	or ''currentColor'' in user agents that do not support the ''invert'' value.
-	The computed value for ''outline-color/invert'' is ''outline-color/invert''.
-	For <<color>> values, see [[css-color-4#resolving-color-values]] in [[!CSS-COLOR-4]].
-	For <<image-1D>> values, see [[css-images-4#stripes]] in [[!CSS-IMAGES-4]].
+	See [[css-color-4#resolving-color-values]]
+	for the computed value of <<color>> values,
+	and [[css-images-4#stripes]]
+	for <<image-1D>> values.
+
+	<div id=valdef-outline-color-invert class=note>
+		Earlier versions of this specification had an additional <code>invert</code> value,
+		performing a color inversion on the pixels on the screen.
+		This is no longer supported,
+		and was removed for lack of implementations
+		(and of intent to implement)
+		in modern user agents.
+		See [[css-ui-3#outline-color]] for details.
+	</div>
 
 
 <h3 id="outline-offset">